The broad objective of this application is to determine the molecular mechanisms behind alpha-MHC down-regulation that occurs during heart failure. Recent data obtained from both animals and humans indicate a considerable loss of alpha-MHC gene product. However, the mechanism behind alpha-MHC down-regulation during heart failure remains virtually unknown. Recently, the PI has cloned and characterized a single-strand DNA-binding protein (PNRB) that plays a repressor role in gene transcription. Interestingly, the PI found that PNRB binds not only to an essential cis-regulatory element of the alpha-MHC gene but also to the coding region of alpha-MHC mRNA. The RNA oligonucleotide corresponding to this coding region has the ability to specifically pull down PNRB from cardiac nuclear extract. Furthermore, cellular levels of PNRB are found to be tremendously high in failing hearts. In light of these observations, the PI believes that PNRB plays a dual role, impairing both transcription and translational regulation of alpha-MHC gene expression in overloaded hearts. In this proposal, experiments have been designed to further explore the significance of PNRB in the control of alpha-MHC expression during heart failure. The PI will examine the role of PNRB in the transcription and translation of the alpha-MHC-reporter gene. The PI will also analyze the physiological significance of PNRB in alpha-MHC expression in a while heart preparation, and on the contractile characteristics of a failing heart.